The strinking advances in peptide chemisry of recent years directed toward parathyroid hormone have resolved many of the basic chemical problems which originally hindered progress in this field. While continuing our basic chemical investigations to resolve critical aspects of structure/activity relations in hormone action which have led to the design and synthesis of several analogues of parathyroid hormone possessing diverse biological properties, we are now devoting increased attention to the mechanisms of hormone interaction with the target tissues and membrane receptors, steps subsequent to receptor binding, the metabolism of the hormones after their release from the sites of their syntheses, and the molecular biology of hormone biosynthesis. The ultimate goal of our unit is the systematic acquisition of sufficient information about hormonal function in mineral ion and bone metabolism, including the control of production and turnover of the hormones and an understanding of their complex and synergistic actions at the target tissues, to permit eventually precise and quantitative analyses of the normal patterns of control of calcium homeostasis and, thereby, to analyze more precisely the pathophysiology of disorders of calcium and bone metabolism.